Are you lost ?
Do you have trouble understanding this document ?
In that case please read the overview provided by the
Introduction to Parser Tools. This document is the
entrypoint to the whole system the current package is a part of.

This command takes the structured form of a syntax error as
thrown by parser runtimes and the input text to the parser which
caused that error and returns a string describing the error in a
human-readable form.

The input text is required to convert the character
position of the error into a more readable line/column format, and to
provide excerpts of the input around the error position.

This command takes the structured form of a syntax error as
thrown by parser runtimes and the input text to the parser which
caused that error and returns a 2-element list containing the line
number and column index for the error's character position in the
input, in this order.

This document, and the package it describes, will undoubtedly contain
bugs and other problems.
Please report such in the category pt of the
Tcllib Trackers.
Please also report any ideas for enhancements you may have for either
package and/or documentation.